Hot piercing mill with skew rolls for the production of seamless metal tubes



' March 3, 1970 c. M ONTAGNA 3,493,096

HOT .PIERCING MILL WITH SKEW ROLLS FOR THE PRODUCTION OF SEAMLESS METALTUBES Filed 0ct'.v20, 1967 l 2 Sheets-Sheet 1 INVENTOR.

CHRLO MONT/76AM March 3, 19-70 C.&MONTAGNA 3,498,096

v MILL WITH {.SKEW ROLLS FOR THE OF SEAMLESS METAL TUBES 301 PIERCING 2Sheets-Sheet 2 raonucwxon and Oct. 20, 196? 4 H nvvawrag C4250 MONTAGNAUnited States Patent Oflice 3,498,096 Patented Mar. 3, 1970 3,498,096HOT PIERCING MILL WITH SKEW ROLLS FOR THE PRODUCTION OF SEAMLESS METALTUBES Carlo Montagna, Via Luciano Manara 15, Milan, Italy Filed Oct. 20,1967, Ser. No. 676,823 Claims priority, application Italy, Nov. 3, 1966,29,542/ 66 Int. Cl. B21b 19/04 U.S. C]. 72-97 6 Claims ABSTRACT OF THEDISCLOSURE This invention relates to a novel hot piercing mill for theproduction of seamless metal tubes from round blooms using skew rolls.

In the novel hot piercing mill one of the rolls is hollow and the otherone, of traditional barrel design, is positioned inside said hollowroll, the bloom to be pierced being positioned between the inner surfaceof the hollow roll and the outer surface of the barrel roll.

DESCRIPTION OF THE INVENTION Having briefly summarized the disclosure,the present invention relates to hot piercing mills with skew rolls forthe production of seamless tubes and more particularly to a new piercingmill with one hollow roll having in the inside the second roll.

In the production of seamless tubes, for the hot piercing of roundblooms (ingots or billets) a skew-rolls mill, Mannesmanns type, havingtwo or more barrel type rolls or similar, is normally used.

It is known that the combined action of the two rolls, while advancingthe bloom with roto-traverse motion, starts also the breaking off(disgregation) of its axial core. Said effect is later completed by theaction of a plug suitably shaped, which is fitted to a bar on theextension of the bloom axis. This plug Widens and smooths the boreproduced by the skew rolling. It is also known that in order to obtainsuch a rate of deformation of the bloom to cause breaking off at thecenter, it is necessary to have the rolls act on the bloom with a strongrolling force. The result of this force is a stress in each element ofthe bloom.

In each cross-section through the bloom, ahead of the position where thebreaking off of the core starts, the unitary compressive stress diagram,along the diameter perpendicular to the direction of the compressiveforce, is a very steep one (with a maximum of the axis of the bloom).

The compressive stresses, which cause the breaking off of the axialcore, are concentrated in a limited central part of the bloom, wherethey reach a high absolute value. We have, therefore, in said part greatdifferences of stress among one point and those immediately adjacent.This (together with the action of ovalization of the bloom due to therolls) causes tearings in the material, which can spread out also tosome distance from the axis and which will not be eliminated by thefurther widening action of the plug, thus originating a defective boresurface.

With the present invention, we have found a remedy for this trouble, asit realizes working conditions suitable for getting a much more flatdiametrical diagram of the compressive stress for the central part. Wehave, i.e., in comparison with the previous case, a lower absolute valueof the stress in correspondence of the axis of the bloom; moreover wehave in the central core, where the breaking off occurs, lowerdifferences between the stress in one point and that in the adjacentpoints. The above mentioned danger of tearing the material is thuseliminated. That (together with a less pronounced action of ovalization)enables to obtain hollow blooms with a sounder inside surface.

According to the present invention the hot piercing mill has one hollowroll, duly profiled on the inner surface, and one traditional barrelroll of known design profiled in agreement with said inner surface,positioned inside said hollow roll in a manner that between the innersurface of the hollow roll and the outer surface of the barrel rollthere is sufficient room for the positioning and working of the bloom.

Objects and advantages of the present invention will be readily apparentfrom the following detailed description, when considered in connectionwith the accompanying drawings in which:

FIG. 1 shows diagrammatically the piercing mill in a cross sectionaccording to a plane normal to the axis of the bloom.

FIG. 2 shows the same mill in cross section according to the horizontalplane II-II; and

FIG. 3 represents the cross section according to the vertical planeIII-III.

With reference to FIGS. 1, 2, and 3, wherein similar referencecharacters indicate like parts, the novel hot piercing mill comprisesessentially the hollow roll 1, the usual barrel roll 2, the round bloom3 to be pierced and the piercing plug 4.

Referring to FIG. 2, roll 1 has an inner convex surface as shown and isjournalled in suitable roller bearings 10 into a casing (not shown inthe figure) equipped with the necessary positioning and control means ofknown type. On roll 1 an annular rotor is fitted, bearing a ring gear 5which is driven through a pinion 6, by a known drive system consistingof gearbox and motor (not shown in the figure).

Again referring to FIG. 2, roll 2 has an outer convex surface which isin agreement with the convex surface of the roll 1 and is journalled onsuitable bearings 8 supported in a fork shaped chock (not shown in thefigure) not connected with the above mentioned casing which is alsoequipped with positioning and control means of known type.

The two rolls have a different speed of revolution, in relation to therespective diameters. They can have a common drive in which case theratio among their respective numbers of revolutions is fixed, or eachroll may have its own drive system and, therefore, an independent speedcontrol. The piercing mill is completed by two fixed guide shoes 7,which serve both to contain the ovalization of the bloom during theskew-rolling, and to keep the bloom in the desired working position.

When the two rolls have a separate drive, it is possible to eliminatethe guides as the bloom position can be controlled acting on the speedcontrol of the rolls. It is clear that (as shown in FIG. 3) also in thepiercing mill object of the present invention, the axes of the two rollshave to be skewed of a certain angle in respect to the axis of the bloom(or mill centerline) in order to obtain the conditions of skew rollingon which process is based.

The size variations of the hollow blooms to be produced can be obtainedeither by varying the relative positions of the two rolls or by dulymodifying their relative speeds, in order to bring the work piece in aposition suitable to the desired diameter, moving its axis out of theplane of symmetry of the mill.

This latter possibility is shown by setting 3 (in shortdashed line) ofFIGURE 1, which represents a hollow bloom with a smaller diameter thanthat of setting 3, which is being worked without altering the relativeposition of the two rolls, but simply moving the bloom axis out of theplane of symmetry of the mill by means of a suitable speed adjustment ofthe two rolls.

Inasmuch as various changes may be made in the form, location andrelative arrangement of the parts without departing from the essentialcharacteristics of the invention, it is to be understood that theinvention is not limited to or by the foregoing disclosure of theexemplary embodiment the inventive scope being defined in the appendedclaims.

What is claimed is:

1. A hot piercing mill with skew rolls for the production of seamlessmetal tubes from a solid bloom, comprising one hollow roll, dulyprofiled in the inner surface with a convex surface, and one traditionalbarrel roll having an outer surface profield with a convex surface inagreement with said inner surface, said barrel roll being positionedinside said hollow roll in a manner that between the inner surface ofsaid hollow roll and the outer surface of said barrel roll there issufficient room for the positioning and working of the bloom.

2. A hot piercing mill with skew rolls for the production of seamlessmetal tubes from a solid bloom, comprising one hollow roll, dulyprofiled in the .inner surface with a convex surface, and onetraditional barrel roll having an outer surface profiled with a convexsurface in agreement with said inner surface, said barrel roll beingpositioned inside said hollow roll in a manner that between the innersurface of said hollow roll and the outer surface of said barrel rollthere is sufficient room for the positioning and working of the bloomwhich is kept in the desired working position by two fixed guide shoes;

3. A piercing mill according to claim 1 further comprising a separatedriving system for each of the two rolls with an independent speedcontrol.

4. A hot piercing mill as set forth in claim 1 further comprising apiercing plug between said inner surface and said outer surface forpiercing the solid bloom during working thereof.

5. A hot piercing mill as set forth in claim 4 which further comprises apair of fixed guide shoes between said inner surface and said outersurface for containing the ovalization of the bloom and the position ofthe bloom during working.

6. A method of producing seamless metal tubes from a solid bloomcomprising the steps of feeding a hot round solid bloom between a convexsurface of a rotating annular roll and a corresponding convex surface ofa barrel shaped roll, rotating the barrel shaped roll within the annularroll on an axis inclined with respect to the Z axis of rotation of theannular roll, and piercing the core 459,752 9/1891 Jackson et al 72-97CHARLES W. LANHAM, Primary Examiner L. A. LARSON, Assistant Examiner

